In order to reduce the level of nitrogen oxides, i.e. NOx, in the exhausts from a combustion engine, prior art recirculates some of the exhausts through a return conduit to the combustion engine's inlet. A return conduit for recirculation of exhausts consists of several pipes and components, such as an EGR-valve and an EGR-cooler, for cooling of the exhausts before they are mixed with air and led back to the combustion engine. The return conduit for the exhausts extends from the combustion engine's hot side, where the exhaust conduit is arranged, to the cold side of the combustion engine, where air is led into the combustion engine. During the operation of the combustion engine the individual pipes and components in the return conduit are subjected to vibrations and thermal loads. In order to avoid creation of excessive strains in the return conduit, prior art connects connecting pipes in the return conduit with contact surfaces, facilitating a certain mobility of the pipes in relation to each other. However, such contact surfaces increase the risk of leakages in the connections between connecting pipes. Prior art uses sealing rings made of wrought iron or steel for sealing between the contact surfaces of adjacent pipes in the conduit. However, it is difficult to create completely sealed connections between the contact surfaces with stiff sealing rings made of metal.
The pipe unit defined above, previously known via SE 535 677 C2, counteracts these disadvantages, since such pipe unit is equipped with a contact surface which, when in a connected state with a contact surface of a connecting pipe, facilitates a mobility between the contact surfaces, and thus a mobility between the pipe unit and the connecting pipe. This mobility substantially prevents the occurring of tensions between the pipe unit and the connecting pipe when they are subjected to mechanical and thermal loads. Even though the contact surface of the pipe unit and the contact surface of the connecting pipe are moveably arranged in relation to each other, they may prevent leakages of the gaseous medium relatively well. Through the existence of a pipe-shaped flexible sealing element, a completely sealed connection between the pipe unit and the connecting pipe may, however, be established. Accordingly, a pipe unit of this type may create a so-called expansion joint with a connecting pipe and thereby achieve a so-called double sealing, since in the event a crack or similar should arise in the pipe-shaped flexible sealing element, the pipe-shaped body is available as an extra security inside of this.
Even though the pipe unit described in SE 535 677 C2 functions well, there is naturally a wish to improve it in some respect.